In a Long Term Evolution (LTE) system, a user equipment (UE) sends uplink control information (UCI) to a base station by using a physical uplink control channel (PUCCH). The UCI includes a scheduling request indicator (SR), hybrid automatic repeat request acknowledgement/negative acknowledgement (HARQ-ACK/NACK) information, that is, HARQ feedback information, and channel state information (CSI). The SR is used by the UE to apply to the base station for uplink scheduling. A downlink HARQ-ACK/NACK is used to indicate a decoding result of downlink-transmitted data and perform HARQ acknowledgement on downlink data sent on a PDSCH. The CSI is used to feed back information related to downlink channel quality, to help the eNodeB perform downlink scheduling.
In a Long Term Evolution Advanced (LTE-A) system, to support higher transmission bandwidth, a carrier aggregation (CA) technology is provided. CA means aggregating two or more component carriers (CC) to support higher transmission bandwidth. In a downlink CA scenario, a base station sends downlink data to a same UE on a plurality of CCs. Correspondingly, the UE needs to support feeding back of HARQ-ACK/NACK information on the plurality of downlink CCs.
A hybrid automatic repeat request (HARQ) is a technology combining a forward error correction (FEC) method and an automatic repeat request (ARQ) method. For an error that cannot be corrected by means of FEC, a receive end requests, by using an ARQ mechanism, a transmit end to retransmit data. The receive end usually uses a CRC check code to detect whether an error occurs on a received data packet. If no error occurs on the received data packet, the receive end sends an acknowledgement (ACK) to the transmit end. If an error occurs on the received data packet, the receive end discards the data packet and sends a negative acknowledgement (NACK) to the transmit end, and the transmit end retransmits the same data after receiving the NACK.
In existing CA that has been standardized, aggregation of a maximum of only five carriers is supported, and in a protocol, HARQ-ACK/NACK information is determined by using a semi-static method. In the semi-static method, when a quantity of configured carriers is less than or equal to 5, a codebook of the HARQ-ACK/NACK information is determined according to the quantity of configured carriers and a transmission mode (TM) and a carrier number of each configured carrier. In this method, when there is a configured carrier that is not scheduled (that is, not actually used for data transmission), or when a quantity of codewords transmitted on a carrier does not reach a maximum configuration, the HARQ-ACK/NACK information is padded with some useless bits.
To greatly increase a quantity of carriers that can be aggregated, the 3rd Generation Partnership Project (3GPP) provides LTE Carrier Aggregation Enhancement Beyond 5 Carriers (eCA). The eCA requires that a maximum of 32 carriers are aggregated and that CSI information of a plurality of carriers can be fed back in one subframe. Therefore, UCI information fed back by using a PUCCH is greatly increased. If HARQ-ACK/NACK information is determined according to the method in the existing protocol, more bits need to be fed back. Consequently, data transmission load is increased, performance of transmitting valid HARQ-ACK/NACK information is affected, and even the HARQ-ACK/NACK information cannot be correctly transmitted. Therefore, how to feed back a large amount of UCI information in an eCA scenario becomes an urgent problem to be resolved.